The Sykes-Picot Agreement was a treaty negotiated secretly between Britain and France (negotiated by Mark Sykes and Francois Georges-Picot, hence the name Sykes-Picot). With a mind to securing European domination of the Middle East following the (presumed) collapse of the Ottoman Empire after WW1. The treaty provided a basis for the establishment of a series of 'mandates' – countries governed by the colonial powers, but not formally made colonies. Administrating countries in this way was significantly cheaper than establishing them as formal colonies.
The Sykes-Picot Agreement conflicted with British promises made to other groups about what would be done with the land. The Balfour Declaration (of 1917) and the McMahon-Hussein Correspondence both pleged land to others; these pledges could not be resolved within the framework of Sykes-Picot.